γ-Fe2O3@SiO2@4-(sulfoamino)butanoic acid as a novel superparamagnetic nanocatalyst promoted green synthesis of 5-(aryl)-5H-spiro[diindeno[1,2-b:2′,1′-e]pyridine-11,3′-indoline]-2′,10,12-trione derivatives
Grafting of 4-(sulfoamino)butanoic acid on superparamagnetic γ-Fe2O3@SiO2 nanoparticles afforded γ-Fe2O3@SiO2@4-(sulfoamino)butanoic acid as a novel heterogeneous nanocatalyst, which was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, vibrating sample magnetometry, field emission scanning electron microscopy, and thermal gravimetric analysis. In this research, we report a convenient and one-pot efficient direct protocol for the pseudo four-component preparation of 5-(aryl)-5H-spiro[diindeno[1,2-b:2′,1′-e]pyridine-11,3′-indoline]-2′,10,12-trione derivatives via cascade condensation reaction of 1,3-indandione and isatins with various aromatic amine in the presence of the catalytic amount of γ-Fe2O3@SiO2@4-(sulfoamino)butanoic acid under green conditions in aqueous media. This procedure offers several advantages such as: very easy reaction conditions, simple work-up, or purification, excellent yields, high purity of the desired product, atom economy, and short reaction times. The superparamagnetic catalyst is magnetically separable and retained chemical stability after recycling for at least five consecutive runs without detectable activity loss.